P. Regenfuss, L. Hartwig, S. Klötzer, R. Ebert, Th. Brabant, T. Petsch and H. Exner
Examples are given for the technical applicability of a novel development of selective laser sintering called “laser micro sintering”.
Abstract
Purpose
Examples are given for the technical applicability of a novel development of selective laser sintering called “laser micro sintering”.
Design/methodology/approach
Together with a specific method to produce powder layers, the controlled application of pulsed radiation for the processing of sub‐μm grained metal powders was exploited to produce micro‐tools with a heretofore unattained structural resolution.
Findings
High resolution micro bodies are displayed. Instruments could be generated which proved to fulfil their designation as grip bits for micro manipulators. The micro‐bodies can be generated detachably from or firmly fixed to the construction substrate. The material of the generated bodies withstands the traction forces when used as an injection mold for polymer casts.
Research limitations/implications
Densities and structural resolutions can still be improved especially with a newly updated version of the equipment. Laser micro sintering of materials, other than metal (e.g. ceramics), has still to be developed. The introduction of the equipment and the technique into the market is on its way.
Practical implications
Micro‐tools can be generated with an overall structural resolution of 30 μm and with all the advantages of a freedom technique.
Originality/value
The paper informs the technical community on a new novel modification of the freeform technique selective laser sintering, demonstrating the solution of some problems that have hampered the progress of metal laser into resolution ranges below 100 μm. It also supplies evidence for the technical applicability.
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P. Regenfuss, A. Streek, L. Hartwig, S. Klötzer, Th. Brabant, M. Horn, R. Ebert and H. Exner
The purpose of the paper is the elucidation of certain mechanisms of laser material processing in general and laser micro sintering in particular. One major intention is to…
Abstract
Purpose
The purpose of the paper is the elucidation of certain mechanisms of laser material processing in general and laser micro sintering in particular. One major intention is to emphasize the synergism of the various effects of q‐switched laser pulses upon metal and ceramic powder material and to point out the non‐equilibrium character of reaction steps.
Design/methodology/approach
Recent results and observations, obtained in development of “laser micro sintering,” are surveyed and analyzed. By breaking down the overall process into relevant steps and considering their possible kinetics, an approach is made towards interpreting specific phenomena of laser micro sintering. Thermodynamics upon heating of the material as well as its photo‐electronic response to the incident radiation are considered.
Findings
The findings corroborate a model whereby short pulses of high intensity provide non‐equilibrium pressure conditions at the location of incidence, that allow for the melting of metal powder with an almost immediate expansion of a plasma and/or vapor bulb. Thereby the molten material is condensed and propelled towards the substrate. A final boiling eruption after each pulse is the reason for the morphology of the laser micro‐sintered surfaces and can prevent oxidation when the process is conducted under normal atmosphere. In sintering of ceramics, the short pulsed and intensive radiation increases the chance to excite the material even with photon energies below the bandgap value and it lowers the risk of running into a destructive avalanche.
Research limitations/implications
Owing to the stochastic character of the respective sintering event, that is initiated by each individual pulse, the gathered data are not suitable yet for the formulation of an exact quantitative function between sintering behavior and laser parameters.
Practical implications
The qualitative findings yield a good rule of thumb for the choice of parameters in laser sintering on a micrometer scale and the model is conducive for advanced interpretation of other phenomena in laser material processing besides sintering.
Originality/value
The kinetics and thermodynamics of laser sintering with q‐switched pulses are approached by a qualitative explanation. The heterogeneous and non‐equilibrium character of the processes is taken into account; this character is often neglected by researchers in the area.
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Linda Ke, Haihong Zhu, Jie Yin and Xinbing Wang
– The purpose of this paper is to report the influence of the peak laser power on laser micro sintering 4-μm nickel powder using Q-switched 1064-nm Nd:YAG laser.
Abstract
Purpose
The purpose of this paper is to report the influence of the peak laser power on laser micro sintering 4-μm nickel powder using Q-switched 1064-nm Nd:YAG laser.
Design/methodology/approach
Experimental study has been performed. Nickel powder with grain size of 4 μm has been utilized. A Q-switching duration of 20-25 μs and rate of 20-40 kHz have been used.
Findings
The peak power intensity is so high that the metal particles and molten pool are blown away, leading to laser micro sintering not being successfully proceeded. The scanning line obtained by continuous-wave (CW) laser looks like a rod owing to balling effect. Using a suitable peak power intensity, a good-shaped sintering line can be obtained because the plasma can protect the molten metal from oxidation, and improve the wettability of the system. In addition, the plasma flattening effect may also contribute to the form of the good-shaped sintering line in pulsed laser sintering regime.
Originality/value
The role of plasma induced by pulsed laser with high peak power intensity has been found during pulsed laser sintering under an ambient environment.
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Haihong Zhu, Linda Ke, Wenjuan Lei, Cheng Dai and Baijin Chen
The purpose of this paper is to investigate the effect of the Q‐switching parameters on the sintering behavior of laser micro sintering Cu‐based metal powder, using Q‐switched…
Abstract
Purpose
The purpose of this paper is to investigate the effect of the Q‐switching parameters on the sintering behavior of laser micro sintering Cu‐based metal powder, using Q‐switched 1064 nm Nd‐YAG laser.
Design/methodology/approach
An experimental study has been performed. Metal powder mixture with Cu and Cu‐P alloy powders has been utilized. Q‐switching duration of 15 μs∼25 μs, rate of 25 kHz∼45 kHz have been used.
Findings
The results show that as the Q‐switching rate and duration increases, the peak laser power decreases and the densification enhances. However, an optimal peak laser power exists and if the peak laser power is too low, the density of the sample is also low. The densification regime of laser micro‐sintering is not only caused by the liquid phase filling the pores, but is also caused by the Cu powder migrating and by coalescence, e.g. including initial stage and intermediate stage of the traditional furnace liquid phase sintering. However, the degree of these stages depends on the peak power and input laser energy.
Originality/value
The effect of the Q‐switching parameters on sintering behavior of laser micro sintering Cu‐based metal powder using Q‐switched 1064 nm Nd‐YAG laser has been obtained. It is found that the densification behavior is Q‐switching parameters dependent, although the average laser power is same. The densification regime of laser micro‐sintering includes initial stage and intermediate stage of the traditional furnace liquid phase sintering, but the degree is Q‐switching parameters dependent.
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Swee Leong Sing, Wai Yee Yeong, Florencia Edith Wiria, Bee Yen Tay, Ziqiang Zhao, Lin Zhao, Zhiling Tian and Shoufeng Yang
This paper aims to provide a review on the process of additive manufacturing of ceramic materials, focusing on partial and full melting of ceramic powder by a high-energy laser…
Abstract
Purpose
This paper aims to provide a review on the process of additive manufacturing of ceramic materials, focusing on partial and full melting of ceramic powder by a high-energy laser beam without the use of binders.
Design/methodology/approach
Selective laser sintering or melting (SLS/SLM) techniques are first introduced, followed by analysis of results from silica (SiO2), zirconia (ZrO2) and ceramic-reinforced metal matrix composites processed by direct laser sintering and melting.
Findings
At the current state of technology, it is still a challenge to fabricate dense ceramic components directly using SLS/SLM. Critical challenges encountered during direct laser melting of ceramic will be discussed, including deposition of ceramic powder layer, interaction between laser and powder particles, dynamic melting and consolidation mechanism of the process and the presence of residual stresses in ceramics processed via SLS/SLM.
Originality/value
Despite the challenges, SLS/SLM still has the potential in fabrication of ceramics. Additional research is needed to understand and establish the optimal interaction between the laser beam and ceramic powder bed for full density part fabrication. Looking into the future, other melting-based techniques for ceramic and composites are presented, along with their potential applications.
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Keywords
Dai Cheng, Haihong Zhu and Linda Ke
This paper aimed to investigate the plasma characteristics of selective laser micro sintering Cu‐based metal powder using spectra method.
Abstract
Purpose
This paper aimed to investigate the plasma characteristics of selective laser micro sintering Cu‐based metal powder using spectra method.
Design/methodology/approach
Temporal and time integrating plasma induced during selective laser micro sintering Cu‐based metal powder with a Q‐switched pulsed YAG laser have been detected and analyzed. Boltzmann plot and Stark broadening of the spectra line are utilized to analyze the electron temperature and density, respectively. The influences of the Q‐switching rate and duration on the plasma temperature and electron density have been investigated.
Findings
The results show that the plasma temperature decreases from 9,600 to 9,000 K with the increase of the Q‐switching rate from 5 to 35 kHz if Q‐switching duration of laser is kept at a constant value. The plots of temporal temperature and electron density show that the electron density varies in a faster speed than plasma temperature and the entire expansion process takes about 700 ns‐1 μs in this experiment. Evolutional images of the plasma plume using Q‐switching rate of 5 kHz and 5 μs have been registered by the ICCD with a 10 ns exposure time, which shows that the plasma plume takes about 100 ns to get to the maximum size and 600 ns to disperse.
Originality/value
The plasma spectra of selective laser micro sintering Cu‐based metal powder have been diagnosed experimentally. The plasma characteristics of selective laser micro sintering Cu‐based metal powder have been analyzed.
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Furkan Ulu, Ravi Pratap Singh Tomar and Ram Mohan
PolyJet technology allows printing complex multi-material composite configurations using Voxel digital designs' capability, thus allowing rapid prototyping of 3D printed…
Abstract
Purpose
PolyJet technology allows printing complex multi-material composite configurations using Voxel digital designs' capability, thus allowing rapid prototyping of 3D printed structural parts. This paper aims to investigate the processing and mechanical characteristics of composite material configurations formed from soft and hard materials with different distributions and sizes via voxel digital print design.
Design/methodology/approach
Voxels are extruded representations of pixels and represent different material information similar to each pixel representing colors in digital images. Each geometric region of a digitally designed part represented by a voxel can be printed with a different material. Multi-material composite part configurations were formed and rapidly prototyped using a PolyJet printer Stratasys J750. A design of experiments composite part configuration of a soft material (Tango Plus) within a hard material matrix (Vero Black) was studied. Composite structures with different hard and soft material distributions, but at the same volume fractions of hard and soft materials, were rapidly prototyped via PolyJet printing through developed Voxel digital printing designs. The tensile behavior of these formed composite material configurations was studied.
Findings
Processing and mechanical behavior characteristics depend on materials in different regions and their distributions. Tensile characterization obtained the fracture energy, tensile strength, modulus and failure strength of different hard-soft composite systems. Mechanical properties and behavior of all different composite material systems are compared.
Practical implications
Tensile characteristics correlate to digital voxel designs that play a critical role in additive manufacturing, in addition to the formed material composition and distributions.
Originality/value
Results clearly indicate that multi-material composite systems with various tensile mechanical properties could be created using voxel printing by engineering the design of material distributions, and sizes. The important parameters such as inclusion size and distribution can easily be controlled within all slices via voxel digital designs in PolyJet printing. Therefore, engineers and designers can manipulate entire morphology and material at each voxel level, and different prototype morphologies can be created with the same voxel digital design. In addition, difficulties from AM process with voxel printing for such material designs is addressed, and effective digital solutions were used for successful prototypes. Some of these difficulties are extra support material or printing the part with different dimension than it designed to achieve the final part dimension fidelity. Present work addressed and resolved such issued and provided cyber based software solutions using CAD and voxel discretization. All these increase broad adaptability of PolyJet AM in industry for prototyping and end-use.
Details
Keywords
Xiaoyong Tian, Dichen Li and Juergen G. Heinrich
The purpose of this paper is to study the rapid prototyping of porcelain products by using layer‐wise slurry deposition (LSD), in order to reduce the time to market of new or…
Abstract
Purpose
The purpose of this paper is to study the rapid prototyping of porcelain products by using layer‐wise slurry deposition (LSD), in order to reduce the time to market of new or customized porcelain products or artworks.
Design/methodology/approach
The properties such as phase composition, microstructure, shrinkage, density, and mechanical strength, of laser sintered (LS) and biscuit fired (BF) samples, before and after post sintering in a furnace, were studied and compared with each other.
Findings
The laser sintered sample was comparable with the biscuit fired sample in porosity, but had just half the mechanical strength of the latter due to the layer‐wise fabrication process. The feasibility of rapid prototyping of porcelain products was validated by the successful fabrication of some porcelain samples, which showed that the relatively low mechanical strength of the laser sintered sample was still high enough for the following handling processes, such as surface glazing and glost firing.
Originality/value
The paper demonstrates the possibility of rapid prototyping of porcelain components and the models produced by using LSD process.
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Abid Ullah, HengAn Wu, Asif Ur Rehman, YinBo Zhu, Tingting Liu and Kai Zhang
The purpose of this paper is to eliminate Part defects and enrich additive manufacturing of ceramics. Laser powder bed fusion (L-PBF) experiments were carried to investigate the…
Abstract
Purpose
The purpose of this paper is to eliminate Part defects and enrich additive manufacturing of ceramics. Laser powder bed fusion (L-PBF) experiments were carried to investigate the effects of laser parameters and selective oxidation of Titanium (mixed with TiO2) on the microstructure, surface quality and melting state of Titania. The causes of several L-PBF parts defects were thoroughly analyzed.
Design/methodology/approach
Laser power and scanning speed were varied within a specific range (50–125 W and 170–200 mm/s, respectively). Furthermore, varying loads of Ti (1%, 3%, 5% and 15%) were mixed with TiO2, which was selectively oxidized with laser beam in the presence of oxygen environment.
Findings
Part defects such as cracks, pores and uneven grains growth were widely reduced in TiO2 L-PBF specimens. Increasing the laser power and decreasing the scanning speed shown significant improvements in the surface morphology of TiO2 ceramics. The amount of Ti material was fully melted and simultaneously changed into TiO2 by the application of the laser beam. The selective oxidation of Ti material also improved the melting condition, microstructure and surface quality of the specimens.
Originality/value
TiO2 ceramic specimens were produced through L-PBF process. Increasing the laser power and decreasing the scanning speed is an effective way to sufficiently melt the powders and reduce parts defects. Selective oxidation of Ti by a high power laser beam approach was used to improve the manufacturability of TiO2 specimens.
Details
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Anand M.B. and Vinodh S.
The purpose of this study is to rank additive manufacturing (AM) processes for microfabrication using integrated fuzzy analytic hierarchy process (AHP)-technique for order of…
Abstract
Purpose
The purpose of this study is to rank additive manufacturing (AM) processes for microfabrication using integrated fuzzy analytic hierarchy process (AHP)-technique for order of preference by similarity to ideal solution (TOPSIS).
Design/methodology/approach
AM technology selection is formulated as multi-criteria decision-making (MCDM) problem and ranking is obtained using fuzzy AHP-TOPSIS. Five candidate processes considered are laser-induced forward transfer (LIFT), microstereolithography, micro-selective laser sintering (micro-SLS), inkjet, micro 3D printing.
Findings
Criteria weights are obtained using fuzzy AHP, and ranking is obtained using fuzzy TOPSIS. The top ranked criteria include material compatibility, geometrical complexity and minimum feature size. The ranking sequence is LIFT > microstereolithography > micro-SLS > inkjet > micro-3D printing.
Research limitations/implications
In the present study, ten criteria and five alternatives are used. In future, additional criteria and alternatives could be considered in line with technological advancements.
Practical implications
The generated ranking enabled the selection of appropriate AM process for microfabrication.
Originality/value
The application of hybrid MCDM approach for ranking AM processes for microfabrication is the contribution of the study.